Power trains, for example, automotive power trains require shaft and bearing seals to prevent lubricants leaking out and to prevent the ingress of contaminants. Seal life depends on, inter alia, the suitability of the chosen seal for the use to which it is put, the degree of care used in installing the seal, the temperatures to which the seal is exposed in use, the nature of the lubricants with which the seal comes into contact, and the condition of the surface(s) with which the seal comes into contact during use. Seal failure will in most cases lead to leakage of lubricants, which is increasingly regarded as unacceptable, and seals which can no longer perform their intended function must normally be replaced. There is thus a need for the life of seals to be prolonged for as long as possible.
International Specification No. WO 85/04896 indicates that labile sulphur-free additives for lubricants can be obtained by treating additives containing labile sulphur with copper, or copper and another material reactive with labile sulphur, or with an olefin, particularly an .alpha.-olefin, .alpha.-olefins containing 4 to 30 carbon atoms, especially 10 to 20 carbon atoms, being preferred. The olefins mentioned in the Examples are all C.sub.15-18 or C.sub.16-18 .alpha.-olefins.
C.sub.15-18 .alpha.-olefins are also the preferred compounds for use in the process described in U.S. Pat. No. 4,228,022. More generally, it is indicated that the olefins preferably contain 10 to 30 carbon atoms, especially 15 to 20 carbon atoms, and may be straight chain or branched.
European Specification No. 151 581 B is concerned with the preparation of lubricating oil additives which have sufficiently low levels of active sulphur to ensure that lubricants containing the additives are non-staining and non-corrosive to copper and similar materials. Olefinically unsaturated compounds containing 8 to 36 carbon atoms are used. The olefinically unsaturated compounds are compounds containing one or more non-aromatic double bonds, and may be linear or alicyclic. .alpha.-Olefins are preferred, particularly C.sub.16-18 .alpha.-olefins, although other types of olefinically unsaturated compounds are referred to.
The reaction of a sulphurized substance with an olefin to reduce the corrosivity of the product is also disclosed in U.S. Pat. No. 4,147,640, which is concerned with the preparation of lubricating oil antioxidant additives which are free from metals and phosphorus, and which have the ability to protect copper-lead bearings from corrosion. The olefins used contain about 6 to 18 carbon atoms and 1 to 3 olefinic double bonds. The preferred compounds are cyclopentadiene dimers and alloocimene.
Other specifications which disclose lubricating oil compositions containing, among other things, oil-soluble sulphur-containing organic compounds are International Specifications Nos. WO 86/04601, WO 86/04602, WO 86/03772 and WO 86/02638, and U.S. Pat. No. 4,664,825. All five of these specifications refer to the possibility of reducing the active or unreacted sulphur content of sulphurized organic compounds by treating the compounds with an alkali metal sulphide. The specifications also indicate that the compositions disclosed show good nitrile seal compatibility.
The applicants have now discovered that the life of nitrile elastomer seals can be significantly enhanced, when lubricating compositions in contact with such seals contain active sulphur, by the inclusion in the compositions of certain olefinically unsaturated compounds. By "active" sulphur is meant sulphur, including elemental sulphur, which attacks nitrile elastomers.
Whilst the problems of seal compatibility and copper corrosion have been addressed by the prior art in relation to sulphur-containing additives, there is still a need for improved or alternative products or processes for improving compatibility of such additives with elastomeric seals, in particular nitrile seals. The problem of seal compatibility seriously impairs the utility of sulphur-containing additives in lubricating oil compositions which come into contact with nitrile seals.